Process for producing dimethyl ether form synthesis gas

This invention was made in the performance of a research and development contract with the U.S. Department of Energy, the contract number being DE-AC22-80PC30021.

The Fischer Tropsch process for converting synthesis gas comprising carbon monoxide and hydrogen into a variety of hydrocarbons and oxygenated hydrocarbons has been investigated for some time, and a variety of products have been produced by this technique. Examples of products include C 2 to C 6 olefins, lights, e.g. C 1 -C 2 paraffins, C 6 to C 10 hydrocarbons e.g. gasoline and kerosene, as well as oxygenated hydrocarbons, such as, methanol, dimethyl ether, various esters, acids and alcohols. Selectivity to a particular product is influenced substantially by the process conditions utilized, e.g. in terms of temperature and pressure as well as the catalyst utilized in the reaction.

U.S. Pat. No. 4,328,129 discloses a Fischer Tropsch process for producing dimethyl ether and methanol in high selectivity by contacting a gaseous mixture of carbon monoxide and hydrogen with a rhodium-molybdenum catalyst, the condition being monitored to favor production of these two materials. In the background portion of the patent, it is indicated that U.S. Pat. No. 3,941,819 discloses the production of dimethyl ether over a calalyst system consisting of platinum supported on alumina.

U.S. Pat. No. 4,098,809 discloses a process for producing dimethyl ether in a Fischer Tropsch process utilizing a methanol synthesis catalyst, such as a copper base or chromium-zinc base catalyst.

U.S. Pat. No. 3,894,102 discloses a process for converting synthesis gas to dimethyl ether and then subsequently to a high octane gasoline. The first stage of the process involves reacting carbon monoxide with hydrogen in the presence of a mixed methanol synthesis and acidic dehydration catalyst. Temperatures from about 300°-700° F., elevated pressures, e.g. up to about 10,000 psig, and space velocities of at least 500 GHSV are used in the first stage to produce dimethyl ether.

U.S. Pat. No. 4,177,167 discloses a process for producing dimethyl ether by the catalyst reaction of carbon monoxide and hydrogen utilizing a mixture of oxides or salts of metals such as aluminum, chromium, lanthanum, manganese, copper or zinc as a catalyst.

U.S. Pat. No. 4,154,751 discloses a series of supported potassium or rubidium-Group 8 metal cluster catalysts for producing a variety of components in a Fischer Tropsch process. Examples of precursor bimetallic cluster complexes include potassium-iron carbonyl compounds, potassium-nickel carbonyl compounds and potassium-platinum carbonyl compounds though the corresponding rubidium complexes are also shown. These catalysts produce predominantly hydrocarbon products with little or no oxygenate selectivity.

Great Britain No. 2,093,365, describes a catalyst consisting of copper, zinc and alumina which is effective for the conversion of synthesis gas to dimethyl ether.

This invention pertains to an improved catalytic process Fischer Tropsch process for converting synthesis gas comprising carbon monoxide and hydrogen to dimethyl ether. The improvement in the Fischer Tropsch Process comprises effecting the reaction in the presence of an alkali metal-manganese-iron carbonyl cluster incorporated onto a zirconia-alumina support.

Some of the advantages associated with the invention are:

dimethyl ether is formed in high selectivity while methane production is low, and

dimethyl ether is formed at significant rates.

As in the prior art conversion of carbon monoxide and hydrogen to dimethyl ether via the Fischer Tropsch Process, a mixture of a carbon monoxide and hydrogen is effected by contacting the mixture with a catalyst under gas phase conditions for a time and temperature sufficient to effect conversion to the product. Typically, the ratio of carbon monoxide to hydrogen, on a molar basis, is from 0.5 to 2 moles carbon monoxide per mole hydrogen.

The temperatures and pressures utilized for carrying out the process are conventional and adjusted within the reaction zone to favor dimethyl ether production as desired. Generally temperatures used in the reaction are within a range from 200° to 400° C., and preferably 225° to 270° C. and pressures are within a range from 100 to 1000 psig, and preferably 300 to 600 psig.

Unlike the prior art the catalyst utilized in the process is a metal carbonyl cluster. K[Fe 2 Mn(CO) 12 ] or other alkali metal salt, e.g., potassium, sodium, lithium, etc., of the anionic [Fe 2 Mn(CO) 12 ] - cluster. An example of such a cluster is represented by the formula:

K[MnFe.sub.2 (CO).sub.12 ]

The carrier substrate for the alkali metal salt of the iron-manganese carbonyl cluster is a high surface area material and can be prepared by reacting a solution of zirconium alkoxide or other alkoxides such as titanium with alumina. The support generally comprises a mixture of zirconia and alumina with 5-30 wt % zirconia. The presence of zirconia in combination with alumina and the combination with the carbon cluster enhances conversion to dimethyl ether, whereas a support comprising essentially alumina, e.g. greater than 95% by weight of the support, favors the production of hydrocarbons.

The catalyst comprising the alkali metal-manganese-iron carbonyl complex supported on a zirconia-alumina support may be prepared in conventional manner which usually involves reacting the metal carbonyl salt with the support. Generally the reaction is effected by suspending the metal carbonyl complex in a liquid carrier, such as diethyl ether, and contacting the support with the suspension. After contact, the sample is dried in vacuum. No further catalyst pretreatment is required. The level of metal carbonyl cluster present on the support is preferably within a range from about 0.5 to 5% by weight.

The following examples are provided to illustrate various embodiments of the invention.

CO/H.sub.2

T °C.

kPa

m.sup.3 /l · h

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1 K[MnFe.sub.2 (CO).sub.12 ]

Ex 1 1 203 2100

598 13

2 " Ex 1 1 251 2100

299 45

3 " Ex 1 1 248 2100

299 60

4 " Ex 1 0.5 247 2100

612 132

5 " Ex 1 1 280 2100

299 158

6 " Al.sub.2 O.sub.3

1 265 2100

295 5

7 " MgO 1 262 2100

596 96

8 " MgO 0.5 277 2100

592 149

9 Co.sub.2 (CO).sub.8

Ex 1 2 242 2100

607 36

10 Fe.sub.3 (CO).sub.12

Ex 1 1 270 2100

201 169

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Product Distribution (wt %)

RUN CO CONV.

C.sub.1

C.sub.2 -C.sub.4

C.sub.5 -C.sub.11

C.sub.12 +

EtOH

PrOH

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1 19.9 12.8

20.6

10.6

0 14.9

31.2

3.4 6.6

2 48.0 7.9

6.5

3.9 0 46.8

19.7

0.6 13.0

3 47.8 19.5

20.4

4.7 0 41.3

16.4

2.7 0

4 34.7 18.0

18.9

0 0 42.8

20.4

0 0

5 58.4 6.9

13.3

0.7 0 65.7

13.5

0 0

6 64.5 18.3

37.3

14.7

11.0

0.8 6.9 9.8 5.9

7 15.6 58.6

29.6

11.8

0 0 0 0 0

8 9.0 54.6

22.6

0 0 0 11.2

7.3 0

9 33.3 24.4

24.4

37.0

13.2

0 0 0.80

0.62

10 3.2 6.7

50.4

34.9

0 1.16

1.92

0 4.77

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Runs 1-5 show good selectivity of DME production since there is very little ethanol and propanol production. Further, since there is little hydrocarbon production, this shows the catalyst and support are well suited to produce oxygenated derivatives from synthesis gas. The conversion observed in Run 1 is low due to process conditions. Runs 6-8 show that when the support was altered having only the K[MnFe 2 (CO) 12 ] active component, the percentage of oxygenates decreased substantially even though there was good conversion, based upon CO. Runs 9 and 10 show the importance of the active metal-carbonyl cluster component for achieving high selectivity to oxygenates.

Runs 6-8--The cluster K[MnFe 2 (CO) 12 ] was supported on Al 2 O 3 and MgO in a manner analogous to that described in Example 2 after pretreating the supports at 200° C. in vacuum. The catalyst testing results are summarized in Table 1, Runs 6, 7 and 8.

The MgO supported catalyst contained 1.32 wt % Fe and 0.92 wt % Mn. The Al 2 O 3 supported catalyst contained 1.70 wt % Fe and 0.77 wt % Mn.

Runs 9 and 10--The [Co 2 (CO) 8 ] was added to the Zr(OPr) 4 /Al 2 O 3 support, prepared in Ex 1 by a method analogous to that described in Ex 1.

The catalyst contained 1.99 wt % Co. The catalyst testing results are shown in Run 9. The Fe 3 (CO) 12 was incorporated in the same way as the Co 2 (CO) 8 . The catalyst contained 0.83% Fe.